Twitching muscles (also called muscle fasciculations or myokymia) are brief, involuntary, visible or palpable contractions of small groups of muscle fibers, appearing as fine, rapid twitches or ripples under the skin, most commonly in the eyelids, calves, thighs, arms, hands, or face. They are usually benign and caused by minor nerve irritation or hyperexcitability of motor neurons, often triggered by everyday factors like stress, anxiety, fatigue, lack of sleep, excessive caffeine or stimulant intake, dehydration, electrolyte imbalances (especially low magnesium, potassium, or calcium), vigorous exercise/overuse, or vitamin deficiencies (e.g., B12). In most cases, they are harmless, intermittent, and self-resolving without weakness, pain, or other neurological symptoms. Less commonly, persistent or widespread twitching can be associated with neurological conditions such as benign fasciculation syndrome, motor neuron diseases (e.g., amyotrophic lateral sclerosis/ALS, though rare and usually accompanied by progressive weakness, atrophy, or cramps), peripheral neuropathy, thyroid disorders, or medication side effects (e.g., certain antidepressants or stimulants).